The directory callib/src/gen contains a number of subroutines for reading and writing the extensions in FITS format spectral and response files. These are summarized below.
| RDPHA1 | Read a spectrum extension |
| WTPHA1 | Write a spectrum extension |
| RDRMF3 | Read the matrix extension |
| WTRMF3 | Write the matrix extension |
| RDEBD3 | Read the channel boundaries extension |
| WTEBD3 | Write the channel boundaries extension |
| RDARF1 | Read the effective area extension |
| WTARF1 | Write the effective area extension |
To use these routines the link line in the makefile should include
-Lftools_dir/host -lcaltools -lftools -lxanlib -lfitsio